Imbalance in rotating bodies and assemblies has been a pervasive problem ever since the invention of the wheel. This familiar problem is characterized by an imbalance in the weight distribution of a body or assembly as it spins about a rotational axis. Depending upon the speed of rotation and other factors, a weight imbalance can cause an undesirable "wobble" which interferes with the smooth rotation of the spinning body. Today, this problem is widespread across a broad range of technologies ranging from automobile wheel hubs to sophisticated high-speed hard disk drive units.
In a conventional hard disk drive unit, information is recorded on concentric tracks of the surface of a rotating magnetic disk using a transducer element. Ordinarily, the transducer is also used for reading the information back from the surface of the moving disk, which itself is driven by an electromagnetic spin motor. In most cases, the disks are clamped to an annular hub which rotates about a central shaft or axis. The combination of the hub and stacked disks is frequently referred to as the disk pack assembly of the drive.
As is appreciated, the process of writing information to the concentric tracks of the disk is made difficult whenever the disk pack assembly is imbalanced, for whatever reason. By way of example, what happens when an imbalance exists is that the normal circular rotation of the disks becomes exaggerated. Instead of writing a track of data in a full, circular ring-shape, the track is written in an oblong pattern. When perfect circular tracks can no longer be written to the disk's magnetic surface, fewer data tracks can fit in the finite space between the inside and outside diameters of the disk. The net result is that weight imbalance in a disk pack assembly compromises the total number of tracks which can be written to a magnetic disk, and thus, the overall recording density is diminished.
A number of methods and apparatus for combating the problem of disk pack assembly imbalance have been tried in the past. For instance, according to one prior art approach, screws are inserted into any of the available threaded holes disposed along the top surface or end cap of the circular spin motor hub. Ordinarily, such holes are present in the top of the spin motor to accommodate screws used in clamping the disk pack in place. Since not all of the available holes in the top of the spin motor are utilized for clamping the disk pack, different sized screws are threadably inserted into the remaining open holes to try and correct for disk pack weight imbalance. The idea, obviously, is to compensate the disk pack by inserting a screw at the precise location that produces an evenly balanced weight distribution.
Unfortunately, there exists a large degree of variability in the individual weights of each of the screws. The variability in the weights of the screws--even those that are machined to high tolerances--makes it very hard to accurately compensate for weight imbalances using this approach. The inconsistent results produced by this method has lead practitioners to search for a new solution to the problem of disk pack imbalance in disk drive units.
As will be seen, the present invention overcomes the drawbacks of the prior art by providing a precision manufactured plug that can be easily inserted into the holes of the spin motor to precisely correct for imbalances in weight distribution. Since the plugs of the present invention can be manufactured in a diversity of precise weights, highly consistent imbalance correction is achieved.